1. Field of the Invention
The present invention relates to electronic devices, and particularly to an electronic device comprising a circuit for generating dying gasp signals.
2. Related Art
The growing requirements for internet data have increased the popularity of broadband access services. Digital Subscriber Line (DSL) technology has become a main broadband access technology in the world due to its convenient deployment, good performance and lower cost.
Asymmetrical Digital Subscriber Line (ADSL) is the most popular kind of DSL technology. In a typical application, a Customer's Premises Equipment (CPE) is usually configured, controlled, maintained and upgraded by a Central Office (CO). The International Telecommunications Union (ITU) standard G.992.1 of ADSL prescribes that when an ADSL CPE runs out of power, the ADSL CPE must generate dying gasp signals, and send the dying gasp signals to an ADSL CO via an Embedded Operation Channel (EOC).
However, if the ADSL CPE is completely without power, it cannot send out dying gasp signals. Therefore power saving elements, for example capacitors, are used for supplying power to generate dying gasp signals. Capacitors with high capacitance are needed in order to supply sufficient power. Thus, there is generally enough time for an ADSL CPE to generate dying gasp signals and send the dying gasp signals to the ADSL CO. Nevertheless, capacitors with high capacitance increase the cost of the ADSL CPE. In addition, the capacitors take up more space on a printed circuit board, and thus make the layout of the printed circuit board problematic. Furthermore, the increased capacitance increases burst currents, and the ADSL CPE is liable to easily break down. Capacitors with high capacitance are also liable to reduce sensibility of power-down detection in the same circuit and delay the immediate use of time for generation of the dying gasp signals.